Media landing zone with recess for texturing features

ABSTRACT

A magnetic data storage medium includes a dedicated transducing head contact zone for engaging an air bearing slider, primarily when the disk is stationary and also during disk accelerations and decelerations. The contact zone has a dual baseline texture, formed by first creating a recessed region within the transducing head contact zone, and then by forming multiple nodules or other texturing features within the recessed region. The texturing features project upwardly from a recessed surface of the recessed region, and also project above an upper surface of the disk by an amount less than the texturing feature height. Consequently, the texturing features are large enough to counteract stiction due to liquid lubricant meniscus formation, yet also have heights sufficiently low relative to the upper surface to allow reduced transducer flying heights. According to a preferred texturing process, the recessed region consists of multiple individual recesses produced by applying a carbon layer to the disk, then forming cavities by selective laser ablation of the carbon layer.

This application claims the benefit of provisional application Ser. No.60/070,029 entitled “Dual Baseline Texture for Guide/StictionPerformance Improvement,” filed Dec. 5, 1997, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the texturing of magnetic data storagemedia, and more particularly to the texturing of dedicated transducinghead contact zones (also called landing zones) of such media to reducetransducing head flying heights while also minimizing stiction.

Laser treated magnetic disks, particularly those textured over areasdesigned for contact with data transducing heads, are known to reducefriction and improve wear characteristics as compared to mechanicallytextured disks. Traditional laser texturing involves focusing a laserbeam onto a disk substrate surface at multiple locations, forming ateach location a depression surrounded by a raised rim as disclosed inU.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan).An alternative, as disclosed in International Publications No. WO97/07931 and No. WO 97/43079, is to use a laser beam to form domes ornodules, rather than rims. In some cases, each of the domes issurrounded by a raised rim. The features can have either circular orelliptical profiles.

Collectively, the texturing features form a texture pattern ordistribution throughout the head contact zone. A particularly preferredpattern is a spiral, formed by rotating the disk at a controlled angularspeed while moving a laser radially with respect to the disk. The laseris pulsed to form the individual texturing features. The disk rotationalspeed and pulsing frequency together determine the circumferentialpitch, i.e., the distance between adjacent texturing features in thespiral. Meanwhile, the radial speed of the laser controls the radialpitch or spacing between subsequent turns of the spiral. Frequently, thecircumferential pitch and radial pitch are approximately the same, e.g.,20-30 microns. This spacing results in multiple texturing featurescooperating to support a data transducing head at rest in the landingzone, given that the length and width dimensions of transducing headsliders typically are in the millimeter range.

The texturing features themselves can be made with a high degree ofuniformity in size and shape, by maintaining a consistent laser power,focal spot size and pulse duration. As transducer glide heights (flyingheights) continue to decrease, particularly below 1 microinch (25 nm),it becomes increasingly difficult for a texture to accommodate the glideheight, and at the same time minimize stiction. The following tableillustrates different measurements of three values, all in nm: anaverage height of multiple texturing features (Rp); the standarddeviation of the height (σ); and the measured glide avalanche. Glideavalanche occurs when a measured signal output exceeds a certainthreshold, indicating that the transducing head is flying “too close” tothe surface.

TABLE Rp σ Glide Avalanche 15.2 1.4 18.8 15.5 1.2 18.2 18.0 1.6 18.818.7 1.1 21.1 19.7 1.8 24.6 19.8 1.6 25.8 23.0 1.5 30.5 23.6 1.5 27.0

From the table, it is seen that to avoid undue risk of collisions of thetransducing head with the texturing features, while at the same timemaintaining a flying height of about 25 nm, the average height of thefeatures should be less than about 20 nm.

At the same time, the need to minimize friction and stiction imposeslimits on the minimum heights of the texturing features. Typically, aliquid lubricant is applied to the surfaces of magnetic data storagedisks, to improve wear characteristics and reduce dynamic friction.However, the liquid lubricant has the undesirable effect of contributingto stiction, the tendency of a data transducing head, once at restagainst a magnetic disk, to adhere to the disk. This provides at leastmomentary resistance when the disk begins to rotate, potentiallydamaging both the disk and the transducing head, and risking loss ofdata.

A primary cause of stiction is the tendency of the liquid lubricant,through capillary action, to flow about and surround the texturingfeatures in contact with an at-rest transducing head, even flowing tothe head itself as indicated in FIG. 1, where h indicates the height ofa data transducing head when at rest upon the texturing features, two ofwhich are shown. The texturing features, nodules or bumps, are flattenedslightly by the head over an area of contact with a radius r. Bycomparison, r_(m) is the radius of the liquid lubricant meniscussurrounding each texturing feature, with each feature having a radius Rat its base. The value d represents the thickness of the liquidlubricant film over surface areas away from the nodules. Thus, ameniscus of the liquid lubricant surrounds each texturing feature,occupying the full height between the transducing head and disk surface,clinging to the transducing head to provide momentary resistance to diskacceleration.

As seen in the chart of FIG. 2, the stiction effect increasesdramatically as the height of texturing features decreases below 12 nm.

In view of the above, one option for achieving a I microinch glideheight while minimizing stiction appears to be maintaining texturingfeature heights within the range of 13-19 nm. However, given the lack ofabsolute precision in laser beam generation and optical components thatfocus and otherwise shape the laser beam, variance in substratematerials and parameters, and variance in the slider bodies thataerodynamically determine transducing head flying heights, the requireddegree of control is not practical. Further, when the heights oftexturing features are reduced, their diameters are reduced as well, andit may be desirable to maintain larger diameter nodules or otherfeatures to enhance structural stability.

Therefore, it is an object of the present invention to provide asubstrate for a data storage medium having a landing zone textured toaccommodate glide heights less than 25 nm, while simultaneouslyminimizing stiction.

Another object is to provide a landing zone surface texture utilizinglarger texturing features with greater heights, in combination withrecessed regions surrounding the texturing features to accommodateliquid lubricant and thereby counteract the tendency of capillary flowtoward a transducing head at rest on the landing zone.

A further object is to provide an improved process for texturingsubstrates and for fabricating magnetic data recording media to exhibitimproved resistance to stiction despite lower transducing head flyingheights.

Yet another object is to provide a data storage medium having improvedwear characteristics and the tendency to afford increased longevity todata transducing heads used in conjunction with the medium.

SUMMARY OF THE INVENTION

To achieve these and other objects, there is provided a substrate for adata storage medium of the type including a data zone for storing dataand a landing zone textured for contact with a data transducing headmaintained in spaced apart relation to the data storage medium duringuse. The substrate includes a substrate body having a substantiallyplanar substrate surface at least over a landing zone thereof. Arecessed region is disposed within the landing zone, and has asubstantially planar recessed surface spaced apart inwardly from thesubstrate surface by a predetermined distance substantially uniformthroughout the landing zone. Multiple texturing features are formed inthe recessed region and are projected outwardly from the recessedsurface by a projection distance which exceeds the predetermineddistance. Consequently, the texturing features project outwardly beyondthe substrate surface of the substrate body.

This texture can be conveniently thought of as a “dual baseline”texture, in that it provides two separate baselines: one with regard totransducer flying height, and the other with regard to meniscusformation. In particular, the meniscus formation or “stiction” baselineis the recessed surface of the recessed region. To reach a transducinghead at rest in the landing zone, a liquid lubricant would be requiredto traverse the height of each texturing feature, beginning at the baseof the texturing feature, i.e., the recessed surface.

In contrast, the baseline for glide height or flying height is thegeometric mean of the substrate surface and the recessed surface. Byforming the recessed region as a small fraction of the landing zone,e.g., one-third of the surface area or less, the geometric mean issubstantially nearer to the substrate surface. Accordingly, thetexturing feature heights, as they relate to transducing head flyingheight, are effectively reduced by a fraction (preferably at leastone-half, more preferably at least two-thirds) of the “predetermineddistance” between the substrate surface and the recessed surface.

Thus, the benefits of reduced transducing head flying height and reducedstiction are simultaneously achieved, and in degrees that can varyaccording to design considerations. For example, by setting a projectiondistance, or texturing feature height above the recessed surface, atslightly more than 12 nm, stiction can be kept acceptably low whileextremely low, sub-microinch flying heights are achieved. Alternatively,the texturing features can be formed to project beyond the substratesurface by slightly less than 20 nm, to maintain an acceptably lowflying height while considerably diminishing the chance for stiction dueto meniscus formation.

Preferably, the “predetermined distance” or separation between thesubstrate surface and recessed surface is at least about 5 nm, and morepreferably is in the range of about 5 to about 10 nm.

To further ensure against meniscus formation, there should be aclearance between each of the texturing features and the nearest edge ofthe recessed region, as measured in directions parallel to the substrateand recessed surfaces. The clearance should be at least 3 nm, and morepreferably is about 5 nm or more.

Another aspect of the present invention is a process for selectivelytexturing a recording medium substrate, including the following steps:

a. providing a substrate body having a substantially planar substratesurface;

b. applying a material layer over the substrate surface at asubstantially uniform thickness, whereby an outer surface of thematerial layer is substantially planar and parallel to the substratesurface;

c. selectively removing portions of the material from the material layerwithin a predetermined zone thereof, to provide a selected region with arecessed surface disposed inwardly of the outer surface of the materiallayer; and

d. forming multiple texturing features throughout the selected region,each texturing feature projecting outwardly away from the recessedsurface and beyond the outer surface of the material layer.

A preferred material is carbon, applied by vacuum deposition to athickness of about 5-10 nm. Then, a laser (e.g., a CO₂ laser) is used toremove the carbon at selected locations or spots. Preferably, the laserablation removes the carbon throughout the thickness of the carbonlayer, thus leaving the substrate body, e.g., a glass ceramic, exposed.As a result, the thickness of the carbon layer provides the uniformseparation distance between the substrate surface and the outer surface.Then, another laser (e.g., a YAG laser) is directed onto the exposedsubstrate surface areas to form the texturing features, preferably in aone-to-one correspondence to the areas of carbon removal, and preferablywith the texturing feature centered within its associatedcarbon-depleted spot or location.

At this stage, texturing of the landing zone is complete. As an option,that portion of the carbon layer spanning the data zone of the disk isremoved.

Next, post-texturing steps of disk fabrication are completed. Theseinclude the application of several further layers to the texturedsubstrate including the data zone and landing zone. These layers includea chromium underlayer, a thin film magnetic recording layer, and aprotective cover layer, typically carbon. These subsequent layers areapplied by vacuum deposition and in substantially uniform thicknesses,such that the outer surface of the protective carbon layer replicatesthe topography of the textured substrate.

Thus, in accordance with the present invention, the landing zone of adata storage medium substrate is provided with separate, spaced apartbaselines with respect to transducer flying height and stiction. Theseparate baselines are provided by forming a recessed region within thelanding zone, and forming texturing features only within the recessedregion. Consequently, the features can have actual heights, with respectto the stiction baseline, sufficient to minimize stiction due tomeniscus formation, yet also have effective heights, with respect to thenon-recessed substrate surface, sufficiently small to accommodatesub-microinch transducer flying heights.

IN THE DRAWINGS

For a further appreciation of the above and other features andadvantages, reference is made to the following detailed description andto the drawings, in which:

FIG. 1 is a schematic view showing part of a magnetic data transducinghead at rest on a data storage disk, within a landing zone of the disk;

FIG. 2 is a chart showing stiction as a function of texturing featureheight;

FIG. 3 is a plan view of a magnetic data storage disk textured inaccordance with the present invention, and a data transducing headsupported for generally radial movement relative to the disk;

FIG. 4 is an enlarged partial sectional view of the magnetic disk inFIG. 3;

FIG. 5 is an enlarged partial top view of the disk, showing part of adedicated landing zone of the disk;

FIG. 6 is a partial side sectional view of the disk, taken in thelanding zone;

FIG. 7 is a schematic illustration of an apparatus used to texture thelanding zone;

FIG. 8 is a schematic side view showing part of a substrate, beforetexturing;

FIG. 9 is a view similar to that of FIG. 8, showing part of a carboncoating removed;

FIG. 10 is a partial top view of the substrate shown in FIG. 9;

FIG. 11 is a partial side view of the substrate, similar to that in FIG.9, after formation of a texturing feature;

FIG. 12 illustrates post-texturing fabrication stages;

FIG. 13 schematically illustrates an alternative embodiment processstep; and

FIG. 14 is a partial top view of a substrate textured according to analternative embodiment approach.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIGS. 3 and 4 a mediumfor reading and recording magnetic data, in particular a magnetic disk16 rotatable about a vertical axis and having a substantially planarhorizontal upper surface 18. A rotary actuator (not shown) carries atransducing head support arm 20 in cantilevered fashion. A magnetic datatransducing head 22 (including magnetic transducer and air bearingslider) is mounted to the free end of the support arm, through asuspension 24 which allows gimballing action of the head, i.e., limitedvertical travel and rotation about pitch and roll axes. The rotaryactuator and the support arm pivot to move head 22 in an arcuate path,generally radially with respect to the disk.

At the center of disk 22 is an opening to accommodate a disk drivespindle 26 used to rotate the disk. Between the opening and an outercircumferential edge 28 of the disk, upper surface 18 is divided intothree annular regions or zones: a radially inward zone 30 used forclamping the disk to the spindle; a dedicated transducing head contactzone 32; and a data storage zone 34 that serves as the area forrecording and reading the magnetic data.

When the disk is at rest, or rotating at a speed substantially below itsnormal operating range, head 22 contacts upper surface 18. When the diskrotates at higher speeds, including normal operating range, an airbearing or cushion is formed by air flowing between the head and uppersurface 18 in the direction of disk rotation. The air bearing supportsthe head above the upper surface. In accordance with this invention, thedistance between a planar bottom surface 36 of head 22 and upper surface18, known as the head flying height or glide height, is about 1microinch (25.4 nm) or even less. Lower flying heights permit a higherdensity storage of data.

For data recording and reading operations, rotation of the disk andpivoting of the support arm are controlled in concert to selectivelyposition transducing head 22 near desired locations within data zone 34.Following a data operation, the disk is decelerated and support arm 20is moved radially inward toward contact zone 32. By the time the diskdecelerates sufficiently to allow head/disk contact, the head ispositioned over the contact zone. Thus, head contact with other regionsof the disk surface is avoided. Before the next data operation, the diskis accelerated, initially with head 22 engaged with disk 16 within thecontact zone. Support arm 20 is not pivoted until the head is supportedby an air bearing, above the contact zone.

Magnetic disk 16 is formed by mechanically finishing an aluminum orglass ceramic substrate disk 38 to provide a substantially flat uppersurface. Typically in the case of A1 substrates, a nickel-phosphorousalloy has been plated onto the upper surface of the substrate disk, toprovide a non-magnetizable layer 40 with a uniform thickness in therange of about 2-12 microns. Following plating, the exposed uppersurface 42 of the Ni—P alloy layer is polished to a roughness of about0.1 microinch (2.54 nm) or less.

After mechanical finishing, substrate surface 42, at least along contactzone 32, is laser textured to provide a desired surface roughness. Lasertexturing involves melting the substrate disk at and near surface 42,forming texturing features as will be described in greater detail below.

Fabrication of disk 16 involves the application of several layers aftertexturing. The first of these is a chrome underlayer 44 with a typicalthickness of about 10-100 nm. Next is a magnetic thin film recordinglayer 46, where the data are stored, typically at a thickness of about10-50 nm. The final layer is a protective carbon layer 48, in the rangeof 5-30 nm in thickness. Layers 44, 46 and 48 are substantially uniformin thickness, and thus upper surface 18 replicates the texture ofsubstrate surface 42.

Laser texturing involves forming discrete nodules (also called bumps ordomes), or crater-like structures in the form of depressions surroundedby raised, rounded rims that are typically circular but can beelliptical, in the substrate disk at surface 42. The size of thetexturing features depends on the level of laser beam energy impingingupon surface 42, the degree of focusing of the laser beam, and theduration or dwell time of the pulse during which the energy is applied.Typically the nodules are formed in a spiral path, having acircumferential pitch governed by the disk rotational speed and laserpulsing interval during texturing. A radial pitch, i.e., the radialdistance between consecutive turns of the spiral path, is determined bydisk rotation and the rate of radial shifting of the laser relative tothe disk, which can involve movement of the disk rather than the laser.The texturing features can be formed with a high degree of uniformity inheight (distance between the nodule or rim peak and the surface on whichthe feature is formed) typically less than about 30 nm. This provides auniform surface roughness, substantially throughout the contact zone.

FIG. 5 is an enlarged view of part of upper surface 18 of disk 16,particularly within contact zone 32. A roughness or texture is providedby multiple nodules 50, spaced apart from one another according to apredetermined circumferential and radial pitch as just discussed.Nodules 50 do not project upwardly (or outwardly) directly from uppersurface 18, however. Rather, each nodule 50 is formed within a cavity ordepression 52, preferably at least approximately centered within itsassociated cavity. Typically, cavities 52 can have a diameter of about20 microns, while the nodules have diameters of about 8-10 nm.

A variety of cavity diameters and nodule diameters can be employed, andeach nodule need not be precisely centered within its associated cavity.

As best seen in FIG. 6, nodule 50 is projected above or outwardly of themajor plane of upper surface 18, so that multiple nodules in concertsupport data transducing head 22 in spaced apart relation to most ofsurface 18 when head 22 is at rest in the contact zone. Also as shown inthis figure, each cavity 52 has a floor or recessed surface 54 spacedapart inwardly from upper surface 18, and a generally upright peripheralwall 56. Nodule 50 need not be precisely centered within cavity 52. Atthe same time, the clearance between nodule 50 and peripheral wall 56,taken horizontally as viewed in FIG. 6, should be at least about 3 nm,and more preferably is at least 5 nm. The clearance is provided toaccommodate the liquid lubricant, in particular to counteract thetendency of the lubricant to form a meniscus about nodule 50 thatproceeds toward transducing head 22 when the head is at rest uponnodules 50.

The primary difference between the texture of contact zone 32 andprevious textures is that nodules 50 project upwardly from recessedsurfaces 54 rather than from upper surface 18. Consequently, the textureprovides two spaced apart baselines, that in previous designs coincide.In particular, each recessed surface 54 determines a stiction (ormeniscus formation) baseline with respect to its associated nodule 50.The flying height baseline is determined by upper surface 18 incooperation with recessed surfaces 54. More precisely, the flying heightbaseline is the geometric mean of surfaces 18 and 54. Because theprimary advantages of the invention arise from the vertical separationbetween the two baselines, it is preferred that the flying heightbaseline be determined primarily by upper surface 18. Such is the casewhen a recessed region, composed of all cavities 52 within the contactzone, occupies less than half of the contact zone surface, and morepreferably occupies less than one-third of the contact zone surface. Aresult of the latter case is shown by a broken line 58 indicating theflying height baseline.

The dual baseline texture permits the use of nodules or other texturingfeatures with heights sufficient to minimize or avoid stiction due toliquid lubricant meniscus formation, and simultaneously allows forsub-microinch transducer flying heights. Either of these advantages maybe emphasized relative to the other. With reference to the foregoingdiscussion of minimum texturing feature heights necessary to avoidmeniscus formation, nodules 50 could have heights slightly greater than12 nm, for example in the range of 15-18 nm. Assuming a verticaldistance of 5 nm between surfaces 18 and 54, the nodules would projectbeyond surface 18 by distances of 10-13 nm, easily accommodatingsub-microinch transducer flying heights, especially if the flying heightbaseline substantially coincides with upper surface 18. Conversely, if aflying height of about 1 microinch is satisfactory and the primary goalis to virtually eliminate stiction due to meniscus formation, noduleswith heights in the range of 20-23 nm are formed. Again assuming 5 nmbetween surfaces 18 and 54, the nodules project above surface 18 bydistances in the range of 15-18 nm.

More broadly, the texturing features project outwardly beyond surface 18by less than about 20 nm. At the other end of the scale, the nodulespreferably project outwardly from surfaces 54 by more than 12 nm. Theseconstraints afford considerable variety, particularly in view of theoptions to provide different separation distances between surfaces 18and 54, and to provide different proportions of contact zone surfacearea occupied by the recessed region.

FIG. 7 schematically illustrates a laser texturing apparatus 60 used toform dual baseline textures in magnetic media substrates such assubstrate disk 38. The device includes a support stage 62 that rotatesabout a vertical axis 64, and a reciprocating support stage 66 on whichsupport stage 62 is rotatably mounted.

Two lasers, both stationary, are disposed above disk 38 and the supportstages: a CO₂ laser 68 and a YAG laser 70. Respective beam shapingoptics are associated with the lasers, including collimating lenses 72and focusing lenses 74 for bringing the laser beams, indicated at 76 and78 respectively, into focus at desired locations on substrate surface 42of disk 38.

In one particularly preferred fabrication approach, a glass ceramicsubstrate disk 38 is first treated in a vacuum deposition process inwhich a uniformly thick carbon layer is applied onto surface 42. Thepreferred thickness of the carbon layer is at least about 5 nm, morepreferably in the range of 5-10 nm. The result of the carbon depositionis a carbon layer 80 of the preferred thickness, shown in FIG. 8.

The coated disk then is placed on rotatable support stage 62, centeredon axis 64. Then, while stage 62 is rotated to achieve a desiredcircumferential speed, support stage 66 is translated to provide thedesired radial velocity. The CO₂ laser 68 generates beam 76 at awavelength with a high affinity for absorption by carbon. As a result,energy applied to carbon layer 80 at a particular spot or locationremains largely confined to that location and extends through thethickness of the layer. As a result, material is removed to leave agenerally circular cavity extending completely through the carbon layerto surface 42. Thus, surface 42 becomes the recessed surface 54 in eachof the cavities. The result of the CO₂ laser treatment is shown in FIGS.9 and 10. Thus, the CO₂ laser is used to create a recessed regioncomposed of multiple cavities 52.

After the cavities have been formed, the substrate disk is given asecond laser treatment, this time using YAG laser 70. The translationparameters (rotation and radial translation) of the CO₂ laser treatmentstage are repeated, so that a single texturing feature is formed withineach of cavities 52. The result is shown in FIG. 1. Also shown in FIG.11 is a texturing feature in the form of a generally circular, roundedrim 82 surrounding a depression 84. This crater-like texturing featureis frequently formed as an alternative to the rounded nodules or bumps,with the laser power and degree of focus largely influencing the shapeof the texturing feature.

After texturing, a series of vacuum deposition stages are completed toform several layers on the substrate disk, including chrome underlayer44, thin film recording layer 46, and protective carbon layer 48. Theresult is shown in FIG. 12.

In the foregoing fabrication process, carbon layer 80 is applied overthe entire disk, covering both data zone 34 and contact zone 32.According to an alternative embodiment process, that portion of carbonlayer 80 covering the data zone can be removed, e.g. by a masking andetching stage, leaving the substrate surface in the data zone exposed asindicated in FIG. 13.

FIG. 14 illustrates an alternative embodiment substrate disk 86,particularly its contact zone. In disk 86, the recessed region isprovided in the form of a single spiral groove 88, formed by operatingCO₂ laser 68 in a continuous wave (CW) mode rather than a pulsed mode,or in the alternative rotating the disk just slightly between successivepulses. An advantage of this approach is that less precision is requiredin the subsequent laser treatment stage that forms texturing features90. A disadvantage is the need to remove a substantially greaterpercentage of the carbon layer.

Thus, in accordance with the present invention, substrates can betextured to accommodate glide heights of less than a microinch, and notonly avoid increasing stiction, but further minimize stiction due tomeniscus formation. Nodules and other texturing features that otherwisewould be too large for a desired glide height, can be used successfullyin the dual baseline texture. Accordingly, lower glide heights andimproved resistance to stiction can be simultaneously achieved.

What is claimed is:
 1. A substrate for a data storage medium of the typeincluding a data zone for storing data and a landing zone textured forcontact with a data transducing head maintained spaced apart from thedata zone during use of the data storage medium, said substrateincluding: a substrate body having a substantially planar substratesurface of the substrate, at least over a landing zone thereof; arecessed region disposed within the landing zone and having asubstantially planar recessed surface spaced apart inwardly from thesubstrate surface by a predetermined distance substantially uniformthroughout the landing zone; and multiple texturing features formed inthe recessed region and projected outwardly from the recessed surface bya projection distance which exceeds the predetermined distance, wherebythe texturing features project outwardly beyond the substrate surface ofthe substrate body.
 2. The substrate of claim 1 wherein: the texturingfeatures project outwardly beyond the substrate surface of the substrateby less than about 20 nm.
 3. The substrate of claim 1 wherein: saidprojection distance is greater than 12 nm.
 4. The substrate of claim 2wherein: the texturing features project outwardly beyond the substratesurface by at most about 15 nm, and said projection distance outwardlybeyond the recessed surface is at most about 25 nm.
 5. The substrate ofclaim 1 wherein: the substrate surface and recessed surface of thesubstrate are spaced apart from one another by at least about 5 nm. 6.The substrate of claim 5 wherein: said substrate surface and saidrecessed surface are spaced apart by a distance in the range of 5-10 nm.7. The substrate of claim 1 wherein: a clearance between each of thetexturing features and a nearest edge of the recessed region, taken indirections substantially parallel to the substrate and surface, is atleast about 3 nm.
 8. The substrate of claim 1 wherein: the recessedregion is comprised of multiple recesses, each recess associated withone of the texturing features.
 9. The substrate of claim 8 wherein: eachof the recesses is at least generally circular, and each texturingfeature is at least approximately centered within its associated recess.10. The substrate of claim 9 wherein: the recesses have diameters ofabout 20 microns, and the texturing features have diameters of about8-10 microns.
 11. The substrate of claim 1 wherein: each of thetexturing features comprises one of: a nodule projected outwardly of therecessed surface; and a raised rim surrounding a depression andprojected outwardly of the recessed surface.
 12. The substrate of claim1 wherein: said substrate body is formed of a glass ceramic materialcoated with a carbon film, said recessed surface comprises a surface ofthe glass ceramic, and said substrate surface comprises a surface of thecarbon film.
 13. The substrate of claim 1 further including: a thin filmrecording layer of a magnetizable material, formed over the substratesurface, the recording layer having a substantially uniform thicknessand thereby tending to replicate a topography of the substrate.
 14. Thesubstrate of claim 13 further including: a chromium underlayer formedover the substrate surface and disposed between the substrate surfaceand the magnetic recording layer, and a cover layer formed over themagnetic recording layer; said underlayer and cover layer being ofsubstantially uniform thickness whereby the cover layer tends toreplicate a topography of the substrate.
 15. A substrate for a magneticdata recording medium, said substrate including: a substrate body havinga substantially planar substrate surface defining a nominal surfaceplane of the substrate; multiple cavities formed in the substratesurface, at least over a predetermined zone of the substrate surfacededicated to contact with a data transducing head, each cavity includinga peripheral wall defining a cavity depth and a cavity surface at leastgenerally parallel to the substrate surface; and multiple texturingfeatures, one texturing feature formed within each of the cavities andprojecting outwardly from its associated cavity surface by a projectiondistance greater than a depth of its associated cavity, and disposed atleast about 3 nm from the peripheral wall of the associated cavity. 16.The substrate of claim 15 wherein: the texturing features projectoutwardly beyond the substrate surface by less than about 20 nm.
 17. Thesubstrate of claim 15 wherein: each of the texturing features projectsoutwardly beyond its associated cavity surface by at least about 12 nm.18. The substrate of claim 16 wherein: each of the texturing featuresprojects outwardly beyond the substrate surface by at most about 15 nm,and projects outwardly from its associated cavity surface by at leastabout 20 nm.
 19. The substrate of claim 15 wherein: each of the cavitysurfaces is spaced apart from the substrate surface by at least about 5nm.
 20. The substrate of claim 19 wherein: the cavity surfaces arespaced apart from the substrate surface by distances in the range of5-10 nm.
 21. The substrate of claim 15 wherein: the cavity surfaces aresubstantially co-planar.
 22. The substrate of claim 15 wherein: saidcavities are substantially circular, and each texturing feature issubstantially centered within its associated cavity.
 23. The substrateof claim 22 wherein: the cavities have diameters of about 20 microns,and the texturing features have diameters of about 8-10 microns.
 24. Thesubstrate of claim 15 wherein: said substrate body is formed of a glassceramic material with a carbon film applied to the glass ceramicmaterial, and wherein the cavities are formed by selectively removingportions of the carbon film.
 25. The substrate of claim 15 furtherincluding: a chromium underlayer applied over the substrate surface, anda thin film recording layer applied over the chromium underlayer, saidunderlayer and recording layer having substantially uniform thicknesseswhereby the recording layer tends to replicate a topography of thesubstrate surface.